Pyridinecarboxylic acid 1-oxides



2,953,572 2 -1 Patented Sept .20, I 1

South Charleston, W. Va., assignors to Union Carbide Corporation, a corporation of New York f No Drawing. Filed Aug. 25, 1958, Ser. No. 757,089 7 9 Claims. or. 260-1295) This invention relates in general to a new series of pyridine oxides and more particularly to pyridinepolycarboxylic acid l-oxides and a, method for their preparation.

In recent years, several methods have been reported in the literature for the preparation of pyridinemonocarboxylic acid l-oxides. These compounds and their derivatives have found use in the stabilization ofperacids and hydrogen peroxide. Nicotinic acid l-oxide, for example, has been preparedby peroxidation of nieotinic acid with hydrogen peroxide and acetic acid. Also by the oxidation of an alkylpyn'dine l-oxide," such'as 4-nitro S-methylpyridine l-oxide, a good yield of the 4-nitronicotinic acid l-oxide can be obtained. Several other methods are known whereby the pyridinemonocarboxylic acid l-oxides can be obtained in good yields.

While the known methods for synthesizing the pyridinemonocarboxylic acid l-oxides gave good results, when such methods were used in an attempt tojprepare the pyridinepolycarboxylic acid l-oxides, no--rea'ction occurred, and the starting pyridinepolycarboxylicacids A further object of the present invention is to provide pyridinepolycarboxylic acid l-oxides which are usefulas stabilizers. r 5 f Another objectisto. provide pyridinepolycarboxylic acid. l-oxides which are useful in the preparation, of polyester condensation resins. 4 a H I Other objects and a' fuller understanding of. theiinvention will be had by referring to the following description and claimspf w if According to the.present -invention,-a series of.new pyridine l-oxides are prepared by a special oxidationtechnique where such compounds could not be-prepared' by the usual peroxidation methods. 7 Y

. The compounds of thisinvention may be illustfated v the following general formula; V 7

and R is' a member selected from the group consistingof hydrogen, lower alkyl, and nitro groups.

Representative of the compounds of the invention are quinolinic acid 1-oxide,lutidinic'"acid 1'-oxide,*2,5-pyri-.- dinedicarboxy'lic. acid' l-oxide, 2,6-pyridinedicarboxylic acidi l-oxide, cincliomeronic acid l-oxide; 3,5- pyridinedi carboxylic acid l-oxide, 2,4,6-pyridin'et'ricarboxylicyacid were quantitatively recovered. Despitethelamountjof' 1 factor that causes a decrease of the electrondensity'at' the neucleophilic center of the compound being oxidized, results in a much slower rate of'oxidation. A'second factor which greatly influences the rate .of'reactionof oxidation is the well-known phenomenon of steric hindrance which, due to the physical structure of adjacent groups, shields or blocks the reactivec'enter. V Both factors, the diminution of electron density atthe electron-rich center and steric hindrance, are'believed to be operative in causing the pyridinepolycarboxylic"acids to be unreactive towards l-oxide formation. The net effect is withdrawal of electrons from the pyridine ring leaving an electron-deficient nitrogen atom. Additionally, Where the carboxy group is in the alpha position to the nitrogen atom, the well-known zwitterion effect can exist where the nitrogen and oxygen of the acid group are bridged through hydrogen bonding.

It would thus appear that due to a combination of several factors, the pyridinepolycarboxylicacids are resistant to oxidation to the corresponding l-oxides. It is therefore an object of the present invention to'provide a new series of new pyridinepolycarboxylic acids 1- oxides and a method for their preparation whereby these compounds are prepared in good yield.

l-oxide', 2,'3*,6-pyridinetricarboxylic acid 1-oxide ,f2,3,5,6- pyridinetetracarboxylic acid l-oxid e, 4-methyl-2,6"-pyri= dinedicarboxylic acid 1;oxide, fl -nitro-2,6-pyridinedicarboxylic acid l-oxide, and the like.

It was found that all of the factors which were discussed above and .whichp revented the peroxidation techni e r m. b n 1tq'n' e yfid nepp r atz boxylic acid l-oxides ifrorn the. corresponding pyridine/ polycarboxylic acids were .tentire1y removed or greatlyf reduced if the acids were reacted. in 'the .formof the metal salt. By employing, for example, the disodiumfi dipotassiumgor othersalt, the resonance effect is probably reversed, since what. was an electron withdrawing P i. Q -.-.fl 4

is now a negative group, l

whichactually repels electrons, thus maintaining creasing the electronic density at the nitrogen atom,"

The steric effect isalso reduced bythe mutual repulsion of the negative carboxy groups, and lastly, hydrogen zwitterion formation I notb n ing. to give, thel possible, lIu. the. practice of basefanexcess of alkali is avoided. Excess of ox I pyridine 1oxide compound separated.

solved in a solution of sodium hydroxide of -a -concen-- tration of from about 5 to about 20 percent by weightq Other alkali hydroxides can be used either'in water or this invention, in order tooxidize the polysodium salt of'the pyridinepolycarboxylic acid,; theacid is taken up in solution and a known {amount of idea: agent (peracid) is"then'added and,'after wa'rmin'gflthe solution for several hours itis cooled, acidified and the other suitable solvent. An excess of peracetic acid in acetic acid or other suitable solvent is then added dropwise, the mixture being maintained at 50 C. While other peracids may be used, such as performic, perbjenzoic and the like, peracetic is preferred. The molar ratio of peracid to the pyridinepolycarboxyli'c'acid is not necessarily critical and can be varied from about 1.25 to about .0, although the molar ratios above and below the aforesaid range can be employed if desired. Reaction temperatures of from about 30 C. to about 100 C. may beused.

During the addition of the peroxidant, additional sodium hydroxide solution is. added simultaneously and in an amount. suiiicient to maintain complete solution and yet avoid taking the solution to alkalinity. Finally, the solution is warmed on a steam bath for from about 1. to 3 hours, cooled to room temperature and the pH adjusted to less than 1 with a. concentrated acid such as hydrochloric. The product is washed, dried and can be recrystallized from aqueous alcohol.

The products of this invention are useful as chemical intermediates, stabilizers for peracid solutions or as monomers for the preparation of condensation resins. For example, a pyridinedicarboxylic acid l-oxide can condense with an alkanediol to give a polyester resin. When used as inhibitors for the peracids all that is required is an inhibiting amount suificient to inhibit the peracid from decomposition. Concentrations of from about 0.01 percent to about 1 percent by weight are preferred.

Preparation of the pyridinepolycarboxylic acids, the starting materials of this invention, can be efiected by methods known to the art. For example, isocincho meronic acid can be synthesized by oxidation of 2-methy1- 5-ethylpyridine with nitric acid.

The following examples are given by way of illustration of the present invention.

EXAMPLE 1 2,5-pyridinedicarboxylic acid l-oxide Isocinchomeronic acid monohydrate (15.0 grams, 0.275 mole) was dissolved in 90 grams of percent aqueous sodium hydroxide and 45 grams of water. To thissolution was added 25 grams of a solution of 45 percent peracetic acid in acetic acid, concurrently with 20 grams additional 10 percent aqueous sodium hydroxide. The reaction was stirred vigorously during this time. (20 mins.), and temperature was 40 C. After stirring for 1 hour more, 16 additional grams of peracetic acid were added, and the mixture heated for 1 hour on the steam bath. After cooling, the solution was acidified with cone. HCl, filtered, and the product washed with cold water and dried. Yield of isocinchomeronic acid l-oxide was 14 grams, (86 percent) of light tan crystals, M.P. 2A-l244 C. A mixed melting point with isocinchomeronic acid showed a marked depression: 2162l8 C. Anal.: Calcd for C H O N- acid equivalent, 91.5; percent C, 45.9; percent H, 2.73; percent N, 7.65. Foundacid equivalent, 91.9; percent C, 46.1; percent H, 3.2; percent N, 7.73.

A sample of this product was decarboxylated by heating in ethylene glycol at 150 C. for 30 mins. to give nicotinic acid l-oxide, M.P. after recrystallization from methanol, 246-248 C. d. (uncorn). Mixed M.P.s of this nicotinic acid l-oxide with nicotinic acid (M.P. 234 C.) and isocinchomeronic acid l-oxide (above) showed marked depressions (199208 C. and 187230 C., respectively) Acid equivalent: Calcd for C H O N 139'; found 143.

EXAMPLE II 2,6-pyridinedicarboxylic acid l-oxide 2,6-pyridinedicarboxylic acid (5.01 grams, 0.03 mole) was dissolved in 30 grams 10 percent aqueous sodium hydroxide and 15 grams water. To this was added 10 4 grams of a solution of 45 percent peracetic acid in acetic acid concurrently with 20 grams additional sodium hy'-' droxide solution. After heating at 60 C. for 1 hour, an additional 5 grams peracetic acid solution was added and the mixture was warmed on steam for an additional hour. After cooling and acidifying with cone. HCl, the product was filtered to 'give 4 grams (73 percent) 2,6-pyridinedicarboxylic acid l-oxide as a white, crystalline product, M.P. 155-157 C. A mixed M.P. with 2,6-pyridinedicarboxylic acid was depressed (151 C.), and a mixed M.P. with picolinic acid l-oxide (M.P. 157-159 C.) was also depressed (116 C.). Anal.: Calcd for C H O N: acid equivalent, 91.5; percent C, 45.9; percent H, 2.73; percent N, 7.65. Found: acid equivalent, 93; percent C, 45.54; percent H, 3.06; percent N, 7.94. A sample of this 2,6-pyridinedicarboxylic acid l-oxide was decarboxylated by heating at 148163 C. for 4 minutes, and the resultant product, recrystallized .from methanol ,to give picolinic acid l-oxide, M.P. and mixed M.P. with authentic picolinic acid l-oxide, 153-.-154 C;

EXAMPLE 111 p 2 Stabilization of peracetic acid solution with 2,6- py'ridinedicarboxylic'acid J-oxide "l Samples of peracetic acid in ethyl acetate (initial mm. 43.7%) were heated at C. in glass vessels. Periodic titrations for peracetic acid gave the following percent by weight of peracetic acid at the time indicated.

acid oxide. V 2. A compound of the general formula:

wherein (n) is a whole positive integer of from 2 to 4 and R is a member selected from the group consisting of hydrogen, lower alkyl, and nitro groups.

3. An unsubstituted pyridinedicarboxylic acid l-oxide.

4. A new composition of matter, 2,5-pyridinedicarboxyilc acid l-oxide.

5. A new composition of matter, 2,6-py dinedicare boxylic acid l-oxide.

6. A process of preparing a compound of the general formula:

wherein (n) is a whole positive integer of from 2 to 4 and R is a member selected from the group consisting of hydrogen, lower alkyl, and nitro groups; which-comprises the steps of preparing the metal salt of said compound;

oxidizing said metal salt with an axidizing agent to the v 2,953,672 5 v pyridinepolycarboxylic acid l-oxide and recovering said References Cited in the file of this patent- UNITED STATESPATENTS 7. A process as claimed in claim 6 wherein the oxidizing agent is a peracid. a i 8. A process as claimed in claim 7 wherein the oxidiz- 5 reenspan p 2,624,655 Greenspan Ian. 6, 1953 mg agent 1s peraceuc acid. 2 663 621 Gr D 22 1953 9. A process of preparing a pyridinepolycarboxylic empan acid l-oxide which comprises the step of preparing the allcali metal salt of a pyridinepolycarboxylic acid, oxidiz- FOREIGN PATENTS ing said salt with a peracid to the pyridinepolycarboxylic 10 734,467 Great Britain Aug. 3, 1955 l-oxide, and recovering said l-oxide. 

1. AN UNSUBSTITUTED PYRIDINEPOLYCARBOXYLIC ACID 1OXIDE.
 5. A NEW COMPOSITION OF MATTER, 2,6-PYRIDINEDICARBOXYLIC ACID 1-OXIDE. 